One summer, fifteen kids innocently wander into a nearby seaside cave. There they meet a strange man who invites them to play an exciting new video game. This game, he explains, pits one lone giant robot against a horde of alien invaders. To play the game, all they have to do is sign a simple contract. The game stops being fun when the kids find out the true purpose of their pact.

Komo's battle takes a shocking turn when the enemy pilot flees for his life...and then comes out of hiding where nobody would have expected. Anko's battle begins not long after, but this time, the entire world is watching. A broadcast crew from her father's TV news show comes along for the ride, letting the secret of Zearth out for good.